Flasher circuit with means for adjusting flash rate and duration

ABSTRACT

A transistorized oscillator circuit for repetitively flashing one or more load lamps on and off. The circuit is adapted for use in hazard warning lights employed at construction sites and operates on a battery power supply. The circuit utilizes standard tolerance components but includes means which permit it to be calibrated to the particular specifications of the user. The circuit also includes switching means for converting it from a flasher circuit to one in which the load lamp burns continuously.

United States Patent Inventor John 1'. Adams Fayettevllle, N.Y.

Appl. No. 831,691

Filed June 9, 1969 Patented June 8, 1971 Assignee R. E. Dietz Company Syracuse, NY.

FLASHER CIRCUIT WITII MEANS FOR ADJUSTING FLASH RATE AND DURATION 16 Claims, I Drawing Fig.

Int. Cl ..II03k 3/281, H05b 39/09 Field of Search 315/200,

[56] References Cited UNITED STATES PATENTS 2,901,669 8/1959 Coleman.. 315/158 3,018,473 1/1962 Rodgers 340/331 3,046,494 7/1962 Root 331/11 1 3,130,349 4/1964 Mallory 315/151 3,478,249 1 1/1969 Ivec 315/205 3,508,167 4/1970 Russell 331/111 Primary ExaminerRoy Lake Assistant Examiner-E. R. La Roche A uorney-Bruns and Jenney ABSTRACT: A transistorized oscillator circuit for repetitively flashing one or more load lamps on and off. The circuit is adapted for use in hazard warning lights employed at construction sites and operates on a battery power supply. The circuit utilizes standard tolerance components but includes means which permit it to be calibrated to the particular specifications of the user. The circuit also includes switching means for converting it from a flasher circuit to one in which the load lamp burns continuously.

FLASHER CIRCUIT WITH MEANS FOR ADJUSTING FLASH RATE AND DURATION CROSS-REFERENCE TO RELATED APPLICATIONS The flasher circuit disclosed herein is substantially the same as the switcl*tg means portion of the circuit disclosed in copending application Ser. No. 774,818, filed Nov. 12, I968 by the same applicant.

BACKGROUND OF THE INVENTION This invention relates generally to flasher circuits forbattery operated hazard warning lights, and has particular reference to a novel circuit of this type having adjustable means for controlling the flash rate and flash duration.

In many of the prior art flasher circuits, the duration of the flash and the flash rate are determined by the current gain of the switching transistor and the values of the associated-circuit capacitance and resistance. These circuits require that the components (transistors, resistor and capacitors) be selected in matched groups if the flash duration and rate are to meet prescribed specifications. Many circuits of this type also utilize a photocell to turn the circuit'on at sunset and off at sunrise, and here again matched circuit components are needed when strict performance requirements are to be met. The need to use matched components generally makes the circuits excessively high in cost, and has the further disadvantage that a circuit which meets one set of specifications may not be of any use where different specifications have been prescribed.

SUMMARY OF THE INVENTION The flasher circuit of the invention is designed to use standard tolerance components together with adjustment means which enable the flash rate and duration to be precisely set to the required specifications. Because standard tolerance components can be utilized, inventory requirements can be reduced; and by obviating the need for matched groups of components, the circuits can be mass produced and then calibrated 'to meet different sets of specifications. In this manner, the cost of manufacture can be substantially reduced.

An important advantage of the circuit arrangement of the invention is that the flash rate and flash duration adjustments are independent of one another so that the making of one of the adjustments does not affect the other. The circuit makes provision for an optional photocell, and it is a further advantage that the photocell can be incorporated and will turn the circuit on and off at the prescribed light levels without affecting flash rate and duration adjustments previously made. Another desirable feature of the circuit is that its operation can be readily modified so that the load lamp burns continuously instead of flashing.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the drawing is a schematic diagram of a flasher circuit embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Having reference now to the drawing, the circuit includes a pair of terminals 6 and 7 for connection to a DC power source and three transistors 8, l and 12. Connected across the terminals 6 and 7 is a series circuit comprising the incandescent lamp 14 that is to be flashed on and off and the collectoremitter path of the NPN transistor 12. The base of transistor 12 is connected through a resistor 16 to the collector of PNP transistor 10, and the emitter of the latter is connected to the positive terminal 6 as shown. The base of transistor is connected through resistor 18 to the collector of NPN transistor 8.

A voltage divider comprising resistors 20, 22 and 24 is connected across the power terminals, resistor 24 being a miniature potentiometer. The emitter of transistor 8 is connected to the junction of resistors and 22. The base of transistor 8 is connected to one side of a capacitor 26, the other side of which is connected to negative terminal 7.

The charging circuit for the capacitor includes a circuit branch which extends from the junction of lamp l4 and the collector of transistor 12 to the side of the capacitor that is connected to transistor 8. This branch comprises series connected resistors 28, 30 and 32, resistor 30 being a miniature potentiometer and resistor 28 having a diode 34 connected in parallel therewith. An additional resistor 36 is connected between the junction of resistors 20 and 22 and an intermediate point 38 on the above-described branch circuit. A second pair of terminals 40 is provided so that an optional photocell 42 can if desired be incorporated in the circuit in parallel with capacitor 26.

The operation of the circuit is as follows: With a power source such as a 6 12 or 18 volt battery connected to the terminals'6 and -7 and switch 44 closed, power will be applied to the components of the circuit including the voltage divider. The voltage divider causes a particular reference potential to be applied to the emitter of transistor 8 which, with capacitor 26 initially uncharged, biases the transistor to the nonconducting state. With transistor 8 off, transistor 10 has no base cur- .rent and also is off, as is transistor 12 for the same reason.

With transistor 12 in the nonconducting state, no appreciable current will flow through the lamp l4 and, therefore, it will also be off. 7

' At the instant that the power is applied, capacitor 26 will start to charge through the low off resistance of lamp 14, through a normally closed switch 45 (to be described) and through resistors 28, 3t) and 32. This will cause the base voltage of transistor 8 to rise with respect to its emitter voltage and when it exceeds the voltage across resistors 22 and 24, transistor 8 will begin to conduct. The collector current of transistor 8 then flow's through the base of transistor 10 and turns it on, and this in turn causes transistor 12 to conduct. With transistor 12 conducting, its collector to emitter voltage drops to a very low value and sufficient current flows through lamp 14 to turn it on.

Turning on transistor 12 also causes resistor 36 to be effectively connected across resistors 22 and 24 which reduces the emitter to negative terminal voltage of transistor 8 and insures that the latter is fully turned on. With transistor 12 and lamp 14 on, capacitor 26 stops charging and starts to discharge through resistor 32 and 30, diode 34 and transistor 12. The diode effectively shoits out resistor 28 with the result that the discharge time is short as compared to the charge time, and I emitter voltage, the transistor turns off and this causes transistors 10 and 12 and lamp 14 to turn off also. With the lamp and transistor 12 off, capacitor 26 again begins to charge through the lamp and resistors 28, 30 and 32 whereby the next cycle is started. Because transistor 12 is not conducting at this point, resistor 36 is no longer effectively connected across resistors 22 and 24 and the original reference potential is reestablished at the emitter of transistor 8. As long as the switch 44 remains closed, the circuit will continue to oscillate in this manner causing the lamp to flash on and off.

The duration of the flash, or on time of the lamp, can be controlled by adjustment of resistor 30 which, as previously noted, is a miniature potentiometer. Thus, the flash duration is determined by the ratio of resistors 30 and 32 to resistor 28, with resistor 32 establishing the lower limit. The flash rate can be controlled by adjustment of the potentiometer 24 because its adjusted value determines the level to which capacitor 26 must charge before transistor 8 starts to conduct and thus determines the flash rate.,The values of resistors 20 and 36 are selected so as to provide a circuit condition that makes the adjustment of the flash rate independent of the flash duration adjustment. In'this manner, by adjusting resistor 30 to obtain the desired flash duration and resistor 24 to obtain the desired flash rate, the circuit can be quickly calibrated to meet prescribed specifications.

It is also a feature of the circuit of the invention that, since the voltage divider consisting of resistors 20, 22 and 24 provides a reference potential at the emitterof transistor 8 that is a fixed fraction of the supply voltage, variations in the latter over a relatively wide range have little effect on either flash rate or flash duration. Another advantage of the circuit is that it will operate on a 6, 12 or 18 volt power supply and, except for the lamp, will not require component changes or circuit recalibrations. Operation of the circuit with anyone of these power supplies has proved satisfactory over a temperature range from F. to 125 F.

As stated above, the auxiliary pair of terminals 40 provide a connection for an optional photocell 42. The cell that is provided is one in which the resistance decreases as the light level increases. Thus, when its resistance is reduced sufficiently by the light, the photocell provides a bypass to the capacitor 26 whereby the voltage across the latter does not get high enough to turn on transistor 8 and the circuit does not oscillate. In darkness, the resistance of the photocell is high enough so that the cell has a negligible effect on the normal operation of the circuit.

It may be desirable under certain conditions to have the hazard warning light in which the above described circuit is employed operate as a steady burning light rather than a flasher. To this end, means including the previously mentioned switch 45 are incorporated in the circuit for modifying its operation so that lamp l4 burns continuously except when shut off by the photocell 42. Switch 45 is a double pole-double throw switch, the other half of which is connected in series with a resistor 46 in a branch circuit extending from one of the photocell terminals 40 to the positive terminal 6 as shown.

When switch 45 is moved to its alternate position, the branch of the capacitor charging circuit that extends from the collector of transistor 12 to the capacitor is disconnected thereby preventing oscillation of the circuit and the resultant flashing of the lamp. Resistor 46 and photocell 42 now form a voltage divider the junction point of which is connected to the base of transistor 8.

in daylight, the resistance of the photocell is so low that the base voltage of transistor 8 is below that required to make it conduct. When the light level drops, the resistance of the photocell increases and this causes the base voltage of transistor 8 to rise with respect to its emitter voltage until it reaches the point at which the transistor starts to conduct. When transistor 8 conducts, transistors 10 and 12 and lamp 14 are also turned on as previously described. Since the circuit cannot be oscillated by the charging and discharging of capacitor'26, lamp 14 will remain on until turned off by a decrease in the resistance of the photocell.

With transistor 12 conducting, resistor 47 is effectively connected across resistors 22 and 24 whereby resistor 47 performs the same function as resistor 36, i.e., it provides regenerative turning on and turning off of the circuit as described above. Resistors 46 and 47 are selected so as to attain the desired light levels for turning the circuit on and off. As will be apparent, moving switch 45 back to the position shown in the drawing will restore the circuit to flashing operation.

lclaim:

1. In an electronic flasher circuit: a pair of terminal for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp load and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collector connected to the base of the second transistor; means connected across the terminals for applying a biasing voltage to the emitter of the fist transistor; a capacitor connected between the base of the first transistor and one of the terminals; and a charging circuit for the capacitor connected between the base of the first transistor and the junction of the lamp load and third transistor collector in said series circuit.

2. A circuit as defined in claim 1 wherein said charging circuit includes variable resistance means for controlling the charging rate of the capacitor. 1

3. A circuit as defined in claim 1 wherein said means for applying a biasing voltage includes variable resistance means for adjusting the level of the biasing voltage.

4. A circuit as defined in claim 1 together with switching means in said capacitor charging circuit for rendering it inoperable.

5. A circuit as defined in claim I wherein the charging of the capacitor alerts the voltage at the base of the first transistor with respect to its emitter voltage so that the transistor switches from a nonconducting to a conducting state, the switching of the transistor to a conducting state being operable to cause the second and third transistors in turn to conduct whereby the lamp load is energized; and means in the circuit connected between the emitter of the first transistor and the junction of the lamp load and third transistor collector that operates when the third transistor is conducting to alter the emitter voltage of the first transistor so that full conduction of the latter is insured.

6. In an electronic flasher circuit: a pair of terminals for connection to a power source; a transistor; means in the circuit, when power is applied to the terminals, to apply a biasing potential to the emitter of the transistor; said last-named means including variable resistance means for adjusting the biasing potential to the desired level; a capacitor connected between the base of the transistor and one of the terminals; means in the circuit to charge the capacitor and thereby alter the potential at the base of the transistor so that it starts to conduct; said last-named means including variable resistance means for controlling the capacitor charging rate; a series circuit connected across the terminals including a lamp load and the collector-emitter path of another transistor; and means in the circuit connected between the collector of the first-named transistor and base of the last-named transistor to cause the latter to conduct when the former is conducting whereby substantially full power is applied across the lamp load causing it to be energized.

7. A circuit as defined in claim 6 together with means connected between the emitter of the first-named transistor and junction of the lamp load and collector of the last-named transistor that operates when the latter is conducting to alter the potential at said emitter whereby full conduction of the first-named transistor is insured.

8. A circuit as defined in claim 6 wherein said capacitor charging means includes a switching device for rendering the charging means inoperable.

9. In an electronic flasher circuit: a pair of terminals for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collectoremitter path connected between the base of the second transistor and the other of said terminals; means in the circuit for applying a biasing potential to the emitter of the first transistor; a capacitor connected between the base of the first transistor and one of the terminals; a charging circuit for the capacitor, including series connected resistors, connected between the base of the first transistor and junction of the lamp and third transistor collector in said series circuit; said capacitor being charged through the lamp and charging circuit, when power it applied across the terminals, to alter the base potential of the first transistor with respect to its emitter potential and cause it to switch from a nonconducting to a conducting state; conduction of the first transistor causing base current to flow in the second transistor whereby it conducts and causes the third transistor to conduct and the lamp to be energized; and resistance means connected between the emitter of the first transistor and collector of the third transistor operable to alter the biasing potential at the emitter when the third transistor is conducting, the altering of the emitter potential of the first transistor in conduction with the altering of its base potential serving to insure full conduction of the transistor.

10. A circuit as defined in claim 9 wherein one of the resistors in the charging circuit is variable to enable the charging rate of the capacitor to be adjusted.

11. A circuit as defined in claim 9 wherein said means for applying a biasing potential to the emitter of the first transistor includes variable resistance means for adjusting the initial level of the biasing voltage.

12. in an electronic flasher circuit: a pair of terminals for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collector connected to the base of the second transistor; a voltage divider connected across the terminals and having a plurality of resistors one of which is variable; the emitter of the first transistor being connected to an intermediate point on the voltage divider; a capacitor connected between the base of the first transistor and one of the terminals; a charging circuit for the capacitor connected between the base of the first transistor and junction of the lamp and third transistor collector, said charging circuit including a plurality of series connected resistors one of which is variable; said capacitor being charged through the lamp and charging circuit, when power is applied across the terminals, to alter the base potential of the first transistor with respect to its emitter potential and cause it to switch from a nonconducting to a conducting state; conduction of the first transistor causing base current to flow in the second transistor whereby it conducts and causes the third transistor to conduct and the lamp to be energized; and resistance means connected between said voltage divider intermediate point and the collector of the third transistor to provide a circuit in parallel with a portion of the voltage divider when the third transistor is conducting.

13. A circuit as defined in claim 12, wherein one of the resistors in the capacitor charging circuit is arranged in the circuit in parallel with a diode that is operable to short out the resistor when the capacitor discharges.

14. A circuit as defined in claim 12, together with a second pair of terminals arranged in the circuit so that an optional photocell connected across the terminals will be in parallel with the capacitor, the photocell being adapted in the presence of sufficient natural light to reduce the voltage across the capacitor to a value at which the circuit will cease to operate.

15. A circuit as defined in claim 14 together with means in the capacitor charging circuit and cooperable with the photocell that can be actuated to cause the lamp to burn continuously when the resistance of the photocell increases due to insufficient natural light.

16. A circuit as defined in claim 15 wherein said last-named means is a double pole-double throw switch.

273 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,584,257 Dated June 8, 1971 Inventor(s) John F. Adams It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Under "Background of the Invention" line 21, "resistor" should be resistors--; Under "Description of the Preferred Embodiment" line 51, "discharge" should be discharged in claim 1, first line "terminal" should be terminals and in claim 9, Col. 5, line 4 "conduction" should be conjunction Signed and sealed this 1 6th day of November '1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GKT T'FSCHALK Attesting Officer Acting Commissioner of Patents 

1. In an electronic flasher circuit: a pair of terminal for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp load and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collector connected to the base of the second transistor; means connected across the terminals for applying a biasing voltage to the emitter of the fist transistor; a capacitor connected between the base of the first transistor and one of the terminals; and a charging circuit for the capacitor connected between the base of the first transistor and the junction of the lamp load and third transistor collector in said series circuit.
 2. A circuit as defined in claim 1 wherein said charging circuit includes variable resistance means for controlling the charging rate of the capacitor.
 3. A circuit as defined in claim 1 wherein said means for applying a biasing voltage includes variable resistance means for adjusting the level of the biasing voltage.
 4. A circuit as defined in claim 1 together with switching means in said capacitor charging circuit for rendering it inoperable.
 5. A circuit as defined in claim 1 wherein the charging of the capacitor alerts the voltage at the base of the first transistor with respect to its emitter voltage so that the transistor switches from a nonconducting to a conducting state, the switching of the transistor to a conducting state being operable to cause the second and third transistors in turn to conduct whereby the lamp load is energized; and means in the circuit connected between the emitter of the first transistor and the junction of the lamp load and third transistor collector that operates when the third transistor is conducting to alter the emitter voltage of the first transistor so that full conduction of the latter is insured.
 6. In an electronic flasher circuit: a pair of terminals for connection to a power source; a transistor; means in the circuit, when power is applied to the terminals, to apply a biasing potential to the emitter of the transistor; said last-named means including variable resistance means for adjusting the biasing potential to the desired level; a capacitor connected between the base of the transistor and one of the terminals; means in the circuit to charge the capacitor and thereby alter the potential at the base of the transistor so that it starts to conduct; said last-named means including variable resistance means for controlling the capacitor charging rate; a series circuit connected across the terminals including a lamp load and the collector-emitter path of another transistor; and means in the circuit connected between the collector of the first-named transistor and base of the last-named transistor to cause the latter to conduct when the former is conducting whereby substantially full power is applied across the lamp load causing it to be energized.
 7. A circuit as defined in claim 6 together with means connected between the emitter of the first-named transistor and junction of the lamp load and collector of the last-named transistoR that operates when the latter is conducting to alter the potential at said emitter whereby full conduction of the first-named transistor is insured.
 8. A circuit as defined in claim 6 wherein said capacitor charging means includes a switching device for rendering the charging means inoperable.
 9. In an electronic flasher circuit: a pair of terminals for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collector-emitter path connected between the base of the second transistor and the other of said terminals; means in the circuit for applying a biasing potential to the emitter of the first transistor; a capacitor connected between the base of the first transistor and one of the terminals; a charging circuit for the capacitor, including series connected resistors, connected between the base of the first transistor and junction of the lamp and third transistor collector in said series circuit; said capacitor being charged through the lamp and charging circuit, when power it applied across the terminals, to alter the base potential of the first transistor with respect to its emitter potential and cause it to switch from a nonconducting to a conducting state; conduction of the first transistor causing base current to flow in the second transistor whereby it conducts and causes the third transistor to conduct and the lamp to be energized; and resistance means connected between the emitter of the first transistor and collector of the third transistor operable to alter the biasing potential at the emitter when the third transistor is conducting, the altering of the emitter potential of the first transistor in conduction with the altering of its base potential serving to insure full conduction of the transistor.
 10. A circuit as defined in claim 9 wherein one of the resistors in the charging circuit is variable to enable the charging rate of the capacitor to be adjusted.
 11. A circuit as defined in claim 9 wherein said means for applying a biasing potential to the emitter of the first transistor includes variable resistance means for adjusting the initial level of the biasing voltage.
 12. In an electronic flasher circuit: a pair of terminals for connection to a power source; a first, second and third transistor; a series circuit connected across the terminals including a lamp and the collector-emitter path of the third transistor; the second transistor having its emitter-collector path connected between one of the terminals and the base of the third transistor; the first transistor having its collector connected to the base of the second transistor; a voltage divider connected across the terminals and having a plurality of resistors one of which is variable; the emitter of the first transistor being connected to an intermediate point on the voltage divider; a capacitor connected between the base of the first transistor and one of the terminals; a charging circuit for the capacitor connected between the base of the first transistor and junction of the lamp and third transistor collector, said charging circuit including a plurality of series connected resistors one of which is variable; said capacitor being charged through the lamp and charging circuit, when power is applied across the terminals, to alter the base potential of the first transistor with respect to its emitter potential and cause it to switch from a nonconducting to a conducting state; conduction of the first transistor causing base current to flow in the second transistor whereby it conducts and causes the third transistor to conduct and the lamp to be energized; and resistance means connected between said voltage divider intermediate point and the collector of the third transistor to provide a circuit In parallel with a portion of the voltage divider when the third transistor is conducting.
 13. A circuit as defined in claim 12, wherein one of the resistors in the capacitor charging circuit is arranged in the circuit in parallel with a diode that is operable to short out the resistor when the capacitor discharges.
 14. A circuit as defined in claim 12, together with a second pair of terminals arranged in the circuit so that an optional photocell connected across the terminals will be in parallel with the capacitor, the photocell being adapted in the presence of sufficient natural light to reduce the voltage across the capacitor to a value at which the circuit will cease to operate.
 15. A circuit as defined in claim 14 together with means in the capacitor charging circuit and cooperable with the photocell that can be actuated to cause the lamp to burn continuously when the resistance of the photocell increases due to insufficient natural light.
 16. A circuit as defined in claim 15 wherein said last-named means is a double pole-double throw switch. 